The present invention relates to apparatus and methods for controlling the direction of drilling of a borehole in a well and more particularly to a steering system for directing three dimensionally the drilling of a bit and still more particularly to a steering assembly with electric power from the surface and communication to and from the surface and which can change bend angle and the direction while drilling.
The conventional practice for drilling a borehole in a well in a controlled direction requires multiple mechanisms to control the direction while drilling. A common prior art tool for controlling the direction of drilling is a bottom hole assembly consisting of the drill bit, stabilizers, drill collars, heavy weight pipe, and a positive displacement motor (mud motor) having a bent housing. The bottom hole assembly is connected to a drill string or drill pipe extending to the surface. The assembly steers by sliding (not rotating) the assembly with the bend in the bent housing in a specific direction to cause a change in the borehole direction. The assembly and drill string are rotated to drill straight.
Another type of prior art tool steers using non-rotating stabilizers, located some distance above the drill bit, to push radially against the side of the borehole with a force, usually constant, so that the bit will drill in the opposite direction at a controlled rate while drilling ahead so that the direction of the hole is altered. This type of steering tool can change direction at a maximum rate of about fifteen degrees per hundred feet of hole drilled and must be run with a rotary drill string or below a mud motor. One such system uses valves and hydraulic fluid to extend adjustable blades engaging the borehole wall to change direction.
Still another prior art steering tool steers using paddles located some distance above the bit. The paddles push of the side of the borehole in a specific direction as the bottom hole assembly rotates in the hole in order to alter the direction of the borehole. This type of steering tool can change direction at a maximum rate of about ten degrees per hundred feet of hole drilled and must be run with a rotary drill string or below a mud motor.
A further prior art steering tool includes a housing with a ball joint and adjustable blades adjacent the ball joint and bit whereby the extension of the blades causes the downhole portion of the housing to bend at the ball joint with respect to the remainder of the bottom hole assembly. Steerable systems, which contact the wall of the borehole to change bend angle or direction, create an undesirable drag against the borehole wall while drilling. This requires additional drilling force on the bit to overcome this drag. Such contact also inhibits the sliding of the bottom hole assembly within the borehole while drilling.
Another method includes a steerable system having wedges, which are actuated by a pressure differential extending the length of the drill string, against cams to drive them out to change drilling direction. Drilling must be stopped to change drilling angle.
The prior art also includes electrically controlled bent subs. These, however, only control the bend in one plane of the tool. Further, the prior art electrically controlled bent subs can not control the direction of the bend without rotating the drill string.
Although various prior art steerable systems can vary bend angle downhole, few can vary both bend angle and direction. None of the prior art tools control both the angle of the bend and the direction of the bend while drilling. Often it is necessary to pull the entire bottom hole assembly out of the hole to change the angle or the direction of the bend.
There are prior art systems which provide electrical power and hydraulics from the surface using an umbilical mounted on the outside of steel coiled tubing. However, such systems do not provide power to the downhole tool directly from the surface through the wall of the coiled tubing.
The present invention overcomes the deficiencies of the prior art.
The steering assembly of the present invention includes a lower housing mounted on an upper housing by a universal joint allowing the lower housing to bend as much as four degrees in any direction. The steering assembly also includes a control mechanism that controls both the angle and direction of the lower housing with respect to the upper housing while under drilling load. Power to the assembly can be provided directly from the surface and the control mechanism can be controlled remotely from the surface. The steering assembly typically is a part of a bottom hole assembly which includes a drilling motor having a power section above the steering assembly and a bearing pack below the steering assembly with a drive shaft extending through the steering assembly between the power section and the bearing pack. A drill bit is connected to the end of the drive shaft.
The universal joint is a constant velocity joint having a knuckle ball connected to the lower housing and mounted within a cage on the upper housing, the ball being a part of a sleeve that connects to the housing of the bearing pack below and has bearings that are captured between the cage and ball by slots and grooves. The universal joint prevents relative rotation between the motor power section and bearing pack.
The control mechanism includes an angle cam that can be attached to or is part of the knuckle ball on the universal joint. The angle cam projects into the upper housing opposite the bearing pack and drill bit. When the universal joint is rotated so that the bearing pack and drill bit move to an angle and offset, the angle cam moves in the opposite direction to the same angle magnitude and to an offset. The angle cam is adjusted by three wedge members equally spaced apart around the circumference of the inside diameter of the upper housing. The wedge members have a tapered surface that makes contact with a radiused surface on the angle cam so that when all of the wedge members contact the angle cam, its position is secured by the axial locations of each of the three wedge members. The angle of contact between the wedge members and the angle cam can be greater or less than a locking taper although a non-locking taper is preferred and is generally 15xc2x0 or more. The three wedge members are disposed within a wedge body and are disposed between the upper housing on the outside and one or more sleeves on the inside. Each wedge member is attached to a drive train. One type of drive train includes one or more hydraulic pistons that move axially inside hydraulic cylinders formed for each piston in the wedge body. The hydraulic pistons and cylinders for each wedge member are a part of a hydraulic amplifier which is a hydraulic force multiplier that increases the force applied to the wedge members from that applied to the upper end of the drive train. The hydraulic amplifier uses one or more hydraulic smaller pistons and cylinders that have an overall area less than the larger pistons and cylinders attached to the wedge member. The smaller piston is attached to a threaded screw that is threaded to a nut disposed inside the wedge body such that the axial position of the threaded rod relative to the wedge body and thus the smaller piston can be changed by rotating the screw. The opposite end of the threaded screw is connected to an expandable/contractible member with a sliding splined connection. The other end of the expandable/contractible member is attached to an electric motor drive shaft. The sliding splined connection includes mating splines which transmit torque while also allowing axial movement. The three electric motors are fixed in position within the upper housing so that they are prevented from movement within the upper housing. The wedge body is also fixed within the upper housing so that there is no movement therebetween. The position of the angle cam is thus controlled by turning on and off each electric motor so that the drive shaft rotates the threaded screw which in turn moves the smaller piston. The movement of the smaller piston causes the larger pistons to move axially due to the hydraulic pressure applied within the cylinder so that the wedge member moves axially either towards or away from the radiused surface of the angle cam.
The entire control mechanism is encapsulated in oil between the upper housing on the outside and the sleeves on the inside. The oil is disposed in a sealed system capable of sealing against differential pressures as high as 2000 psi from the inside to the outside diameter. A flexible bellows of either reinforced elastomer or metal is attached to the end of the angle cam and to the lower end of the sleeve in the upper housing to form a chamber for housing the oil in the system. Also a floating compensating piston is disposed above the electric motors and includes a spring piston which produces a small increase in pressure inside the oil chamber so that possible drilling mud intrusion is reduced. That portion of the cylinders between the small and large pistons is an independent closed system in communication with a pressure relief system.
The bottom hole assembly is preferably connected to composite coiled tubing extending to the surface where electrical conductors and data transmission conductors in the wall of the composite coiled tubing are connected to a power supply and surface processing equipment respectively. The electrical conductors provide power to the steering assembly and the data transmission conductors provide communication between the surface and the steering assembly. Data from the steering assembly is transmitted to the surface where it is processed by the surface processing equipment and commands may then be transmitted to the steering assembly from the surface to, for example, adjust the bend angle and direction of drilling. The steering assembly may also transmit back to the surface verification of the change in bend angle and direction.
Other objects and advantages of the invention will appear from the following description.